Readily defibered pulp product

ABSTRACT

A wet-laid wood pulp product containing cellulose pulp fibers and elongate precipitated calcium carbonate having a diameter of 0.015 to 0.6 microns at its maximum diameter and a length of 1 to 10 microns and the calcium carbonate being incorporated within the sheet and a method for making the product.

CROSS-REFERENCE TO RELATED APPLICATION

Related patent application includes U.S. patent application Ser. No. ______ (Attorney Docket Number 26643), filed Dec. 31, 2008.

FIELD OF THE INVENTION

The invention is related to a wet-laid wood pulp product containing elongate sub-micron diameter precipitated calcium carbonate and a method for making it.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-2 are photomicrographs of an elongate sub-micron diameter precipitated calcium carbonate.

FIGS. 3-6 are photomicrographs of cross sections of a pulp sheet showing the location of the elongate sub-micron diameter precipitated calcium carbonate in the pulp sheet.

FIG. 7 is a plot of fiberization (Kamas) energy for a control and the additives.

FIG. 8 is a graph of fiberization (Kamas) energy vs. ash content of the pulps

FIG. 9 is a plot of dry bulk at 0.6 kPa for a control and for the additives.

FIG. 10 is a plot of dry bulk at 2.5 kPa for a control and for the additives.

FIG. 11 is a plot of wicking time for a control and for the additives.

FIG. 12 is a plot of wicking rate for a control and for the additives.

FIG. 13 is a plot of wet bulk at 2.5 kPa for a control and for the additives.

FIG. 14 is a plot of resat bulk at 2.5 kPa for a control and for the additives.

FIG. 15 is a plot of capacity for a control and for the additives.

DISCLOSURE

Fluff wood pulps are used as the absorbent layer in disposable diapers, sanitary napkins, and similar absorbent hygienic products. The cellulose pulp of the invention may be made using conventional kraft, sulfite, chemithermomechanical or other well known processes. The furnish can be from any of various cellulose containing raw materials. Most usually these will be deciduous hardwoods, coniferous species, usually termed softwoods; or mixtures of these materials. A preferred pulp is a bleached softwood kraft pulp that would normally be intended for ultimate use as absorbent fluff.

Chemical pulp is prepared by chemically treating cellulosic materials, such as softwoods and hardwoods, to remove their lignin fraction and produce a cellulosic pulp suitable for making paper and related non-woven products. Foremost among the chemical processes are the well-known Kraft and sulfite pulping processes. In the Kraft pulping process, a cellulosic source such as wood chips is digested with an alkaline pulping liquor containing sodium hydroxide and sodium sulfide; while the sulfite process, as the name implies, employs a sulfurous acid solution of an alkali or alkaline earth metal sulfite to effect lignin removal. All known processes also generally rely on some type of post-digestion bleaching to obtain additional lignin removal, and increase the whiteness and brightness of the pulp to enhance commercial acceptance

After the wood chips are digested and the resultant fibers bleached, the fibers are formed into a wet-laid pulp mat. In this operation, the fibers enter a headbox where they are mixed with water and any chemicals that need to be added to the pulp. The fibers exit the headbox onto a moving screen, known as a wire through which the water in the web is drained both by gravity and by vacuum. This step, known in its initial stage as formation, is usually accomplished by passing an aqueous dispersion of a low concentration of pulp (e.g., 0.5% to 1% by weight solids is typical) over the wire. This wire, assisted in certain situations by vacuum or suction, increases the consistency of the mat or web to approximately 20 to 35 weight percent solids.

The mat or web is then compressed or squeezed in a “press section” to remove additional water. This is usually accomplished by felt presses, a series of rollers each having a felted band for contact with the mat or web. These presses remove additional free water and some capillary water, thus resulting in an increase in consistency of the mat or web to a range of about 30 to 60 weight percent. As is well known, in making fluff pulp sheet, less pressure is applied in this portion of the process than normally would be encountered in conventional paper-making, thus less water is removed in this section. Less pressing is done so as to facilitate subsequent comminution of the fluff pulp sheet to the defibrated fluffed pulp.

Following the press section, the pulp sheet is then dried in a dryer section. Because a reduced amount of water was removed in the press section, more moisture must be removed from the sheet in the dryer section than generally is necessary in paper-making. In the drier section, the remaining water content of the pulp sheet is reduced to obtain a pulp consistency which typically ranges between about 88 to 97 weight percent (3 to 12 weight percent moisture), more usually between 90 to 94 weight percent (6 to 10 weight percent moisture). The wet-laid cellulose pulp fibers form into a sheet and attach to each other at contact points by hydrogen bonds. This process is called wet forming.

In the United States it is most typically a fully bleached southern pine kraft process pulp produced in relatively heavy caliper, high basis weight sheets. The product is rewound into continuous rolls for shipment to the customer. Since the rolls of product are intended to be later reprocessed into individual fibers, low sheet strength is desirable and typically little or no refining is used prior to sheeting. The requirements for surface uniformity and formation are similarly moderate.

Absorbent products are formed by dry-fiber air-laid techniques. The pulp rolls are broken into dry fibers which are then conveyed by to a forming station where they are formed into the absorbent product. The pulp roll is broken into individual fibers by disintegrating or comminuting devices such as hammer mills. The energy required for disintegrating the pulp roll into individual fibers is large and a major expense of an absorbent product plant.

In the absorbent product the pulp fibers serve as wicking agents to wick liquid away from the point of insult to other areas of the diaper and also to absorb some of the liquid.

The present invention is a cellulosic wet-laid fluff pulp product treated with elongate sub-micron diameter precipitated calcium carbonate and the method of its manufacture. The product can be converted from sheeted or roll form into individual fibers with significantly reduced fiberization energy input and the fibers in the air-laid product have wicking similar to untreated fibers and have good drape as shown by Gurley stiffness.

The pulp products of the present invention are clearly differentiated from products intended as letter, book, magazine, or similar papers. The caliper of a pulp sheet is 0.02 to 0.08 inches (0.051 to 0.203 cm). The basis weight of the products of the present invention may be as low as about 200 g/m² to 1000 g/m². The fiber will most usually be unrefined or only lightly refined although the invention is not so limited. Where a high surface area product is desired the fiber will normally be significantly refined. The pulp products are unsized is such as to clearly distinguish them from ordinary papers which might contain high amounts of sizing agents. The products of the present invention are unsized and the strength properties such as tensile, burst, and tear strength, which are considered essential in papers, are generally much lower. Pulp is normally not used in its roll form. It is disintegrated back to fibers, either by a disintegrating device such as a hammer mill, if the fibers are to be air laid, or in a broke tank with water if the fibers are to be wet-laid into paper.

Pulp used for papermaking is usually relatively highly refined to develop web strength. The caliper of a paper sheet is 0.003-0.0175 inches (0.002-0.045 cm). The basis weight of paper is normally based on 500 sheets of paper at the standard uncut size for that type of paper. These have been converted to grammage. To compare a pulp sheet and a paper sheet the basis weight of paper has for this purpose been converted to the basis weight of a single sheet of paper. The basis weight of a single sheet of paper is 0.072 to 0.976 g/m² . . . Good strength is essential. Papers are normally sized to improve ink holdout and other printing properties.

The cellulose pulp of the invention may be made using conventional kraft, sulfite, chemithermomechanical or other well known processes. The furnish can be from any of various cellulose containing raw materials. Most usually these will be deciduous hardwoods, coniferous species, usually termed softwoods; or mixtures of these materials. A preferred pulp is a bleached softwood kraft pulp that would normally be intended for ultimate use as absorbent fluff. While so-called “dissolving pulps” may be used these are not preferred because of their low yield and resultant much greater cost. Never-dried or once-dried may be used to form the wet-laid sheet of pulp.

In the present application elongate sub-micron diameter precipitated calcium carbonate is added to the slurry of cellulose pulp fibers in the headbox and is combined with the pulp in the pulp sheet during its formation and drying so that the calcium carbonate is incorporated into the wet-laid pulp sheet.

Normally retention aids such as Nalco 71708 and similar products are required to attach calcium carbonate or other materials to cellulose pulp fibers. No retention aid is needed for the attachment of the elongate sub-micron diameter precipitated calcium carbonate to the fibers. The calcium carbonate attaches directly to the fibers.

The calcium carbonate is elongate sub-micron diameter precipitated calcium carbonate. It has a diameter at its maximum diameter of 0.015 to 0.6 micron. In one embodiment it has a diameter at its maximum diameter of 0.015 microns to 0.06 micron. In another embodiment it has a diameter at is maximum diameter of 0.2 to 0.45 micron. In another embodiment it has a diameter at is maximum diameter of 0.15 to 0.25 microns. In one embodiment it has a length of 1 to 10 microns. Its diameter may vary along its length and it may be narrower at its ends than it is at a point between its ends. Elongate sub-micron diameter precipitated calcium carbonate may be in three forms, a short form having a length of 1 to 3 microns, and medium form having a length of 3 to 6 microns, and a long form having a length of 6 to 10 microns. The short form usually averages 2 microns in length and the medium form usually averages 4 microns in length, and the long form usually average 8 microns in length. Each of these forms may have any of the diameters noted above.

Several companies provide the elongate sub-micron diameter precipitated calcium carbonate. NanoMaterials Technology Pte Ltd (NMT) provides an elongate precipitated calcium carbonate made using the high gravity reactive precipitation (HGRP) technology platform. It has a diameter of 0.015 to 0.06 micron at its largest diameter with an average diameter at its largest diameter of 0.045 micron.

Solvay, S. A. provides an elongate precipitated calcium carbonate that has a diameter of 0.25 to 0.45 micron at its largest diameter with an average diameter at its largest diameter of 035 micron. It is sold under SOCAL® 90A, NZ or P2E. It has an aragonite crystal form and is ortho-rhombic. Solvay, S. A. also provides another elongate precipitated calcium carbonate that has a diameter of 0.15 to 0.25 micron at its largest diameter with an average diameter at its largest diameter of 0.2 micron. It is sold under SOCAL® P1V, P2, P2V, P3E, 93V, 94V, NP, N2, N2R or P2PHV. It has a calcite crystal form and is scalenohedral.

Elongate sub-micron diameter precipitated calcium carbonate is shown in FIGS. 1 and 2. The magnification in FIG. 1 is 2000 times; the magnification in FIG. 2 is 10,000 times.

For the purposes of this application sub-micron diameter precipitated calcium carbonate is precipitated calcium carbonate 0.015 to 0.6 micron in diameter at its maximum diameter and 1 to 10 microns in length. An embodiment of the sub-micron diameter precipitated calcium carbonate has a diameter at its maximum diameter of 0.015 to 0.45 micron. Another embodiment of the sub-micron diameter precipitated calcium carbonate has a diameter at its maximum diameter of 0.015 to 0.35 micron. An embodiment of the sub-micron diameter precipitated calcium carbonate has a length of 1 to 3 microns. Another embodiment of the sub-micron diameter precipitated calcium carbonate has a length of 3 to 6 microns. Another embodiment of the sub-micron diameter precipitated calcium carbonate has a length of 3 to 10 microns.

The elongate sub-micron diameter precipitated calcium carbonate is added to the slurry in the headbox with any other chemicals prior to the formation of the mat. Consequently the sub-micron diameter precipitated calcium carbonate is throughout the mat. This can be seen in FIGS. 3 through 6 which are cross sections of the pulp sheet. The sub-micron diameter precipitated calcium carbonate is white and remains elongate.

The amount of elongate sub-micron diameter precipitated calcium carbonate added to the pulp may be from 3 to 45% of the dry weight of the pulp.

The purpose of the elongate sub-micron diameter precipitated calcium carbonate is to provide a sheet that requires less fiberization energy than a pulp without the elongate sub-micron diameter precipitated calcium carbonate or other similar fiberization agent when the pulp sheet is comminuted and to provide wicking that is the same or close to the wicking of an absorbent product as a pulp without the elongate sub-micron diameter precipitated calcium carbonate. Although retention aids may be used if desired there is no need to use retention aid when using sub-micron diameter precipitated calcium carbonate.

The energy required to defiberize the pulp sheet may be reduced by as much as 30% from a pulp without sub-micron diameter precipitated calcium carbonate or similar fiberization agent when a target of 5% by weight of a elongated sub-micron diameter precipitated calcium carbonate is mixed in the pulp sheet. The decrease may be as much as 50% from a pulp without sub-micron diameter precipitated calcium carbonate or similar fiberization agent when a target of 10% by weight of elongate sub-micron diameter precipitated calcium carbonate is mixed in the pulp sheet.

The elongate sub-micron diameter precipitated calcium carbonate has better fiberization characteristics than a cubic shaped nano precipitated calcium carbonate. The cubic shaped nano precipitated calcium carbonate has substantially the same fiberization energy as a pulp that does not have any cubic or elongate sub-micron diameter precipitated calcium carbonate.

The addition of elongate sub-micron diameter precipitated calcium carbonate reduces the Gurley stiffness. An addition of a target of 10% by weight of the weight of the pulp reduces the Gurley stiffness by around 25%. An addition of a target of 40% by weight of the weight of the pulp reduces the Gurley stiffness by around 83%.

The shape of the elongate sub-micron diameter precipitated calcium carbonate does not appear to matter. The examples show the wicking and fiberization energy characteristics to be similar.

In the method of making the wet laid cellulose pulp sheet the cellulose pulp fibers and elongate sub-micron precipitated calcium carbonate are added to a headbox. The cellulose pulp fibers and elongate sub-micron precipitated calcium carbonate may be mixed before being added to the headbox or may be mixed in the headbox. In one embodiment the amount of elongate sub-micron precipitated calcium carbonate is 3 to 45 percent of the weight of the cellulose pulp fiber. In another embodiment the amount of elongate sub-micron precipitated calcium carbonate is 3 to 15 percent of the weight of the cellulose pulp fiber. Retention aid need not be added though it can be added if desired. The mixture is placed on a wire and the water is pulled from the sheet by vacuum, forming a wet sheet comprising the cellulose pulp fibers and the elongate sub-micron precipitated calcium carbonate. The elongate sub-micron precipitated calcium carbonate is incorporated within the sheet among the cellulose fibers. It has been found that the elongate sub-micron precipitated calcium carbonate attaches to the fibers without the need for retention aid. The wet-laid sheet is usually pressed to remove more water and is then dried. The sheet usually contains from 6 to 12% water.

In the examples that follow:

Fiberization energy requirement is determined using a laboratory scale hammermill instrumented to measure power necessary to fiberize a given weight of pulp. The mill used in the following tests was a Kamas Laboratory Mill, Model H01, manufactured by Kamas Industri, AB, Vellinge, Sweden. The breaker bar clearance of the mill was set at 4.0 mm, the screen size was 19 mm, and rotor speed was adjusted to 3024 rpm. Samples were conditioned at 50% R.H. for a minimum of 4 hours prior to testing. The samples were cut into strips 5.0 cm wide and as long as the sample would permit. Sufficient strips were cut to yield about 150 g of fiberized pulp. Basis weight of the samples was previously determined and the hammermill feed roller speed was adjusted to achieve a target feed rate of 2.80 g/sec

Water absorption rate was determined by using the automatic fluff absorption quality (FAQ) test. The fluff is first formed into an air formed pad within a cylinder 16 cm long and 5.7 cm in diameter having a wire screen at the bottom. The tared cylinder is placed on a balance and pad weight adjusted to 4.0 g by carefully removing any excess fiber from the top with tweezers. The pad height is measured under a no-load condition and the dry bulk under no load is calculated. A 2.5 kPa pressure is applied to the pad, the pad height is again measured and the dry bulk under load is calculated. The bulk is calculated as cubic centimeters per 1 gram. The pad within the cylinder is then placed in the tester and a 2.5 kPa pressure is applied. This is done by lowering a 150 g plunger onto the fluff mat. Water is then introduced at the base of the pad so that the water just touches the screen at the bottom of the pad. Wicking time is the time it takes water to wick through from the bottom of the loaded pad to the top of the loaded pad. The height of the wetted pad is then measured. The wicking rate is the wicking time divided by the average of the loaded dry bulk height and the loaded wet bulk height [(loaded dry bulk height+loaded wet bulk height)/2], and is reported in mm/second. The load is then removed and the fluff is allowed to absorb as much water as possible in the no-load condition (60s). No-load (Resat) wet height/bulk is then measured. The Plexiglas tube containing wet fluff is moved to a balance and weighed to calculate how much water was absorbed. The dry tube tare weight is included in the calculation. The fluff pad initially weighed 4 g dry, but absorption capacity is reported as gram of water/gram of fluff.

The pulp used in the examples in this application is a bleached southern pine kraft wood pulp from southeastern U.S. pulp mills. This grade is produced as a market fluff pulp. The NB-416 grade is sold by Weyerhaeuser Company from its New Bern, N.C. mill. The CF-416 grade is sold by Weyerhaeuser Company from its Columbus, Miss. mill. This grade is produced as a market fluff pulp and was used both as a control material and as a base material in all of the examples in the application. The elongate sub-micron diameter precipitated calcium carbonate or other additive was added to and mixed with the pulp prior to making the handsheet. In the following examples, a target means that amount was targeted for addition but the actual amount added was approximately the targeted amount. For example a target of 5% means approximately 5% was added.

EXAMPLE 1

Hand sheets were made on a 12″ by 12″ handsheet former using once dried NB 416 pulp at a targeted basis weight of 750 g/m². The results of the comparison are shown in Table 1. In column 1, the control was once dried once dried NB 416 pulp. In column 2, a target of 5% elongate sub-micron diameter precipitated calcium carbonate from NanoMaterials Technology having a mean length of 4 microns was added to the once dried NB 416 pulp. In column 3, a target of 10% elongate sub-micron diameter precipitated calcium carbonate from NanoMaterials Technology have a mean length of 4 microns was added to the once dried NB 416 pulp. In column 4, a target of 5% cubic shaped precipitated calcium carbonate have a mean length of 4 microns was added to the once dried NB 416 pulp. In column 5, a target of 10% cubic shaped precipitated calcium carbonate have a mean length of 4 microns was added to the once dried NB 416 pulp. The amount of calcium carbonate added was based on the total weight of the sheet. No retention aid was used.

TABLE 1 1 2 3 4 5 Basis weight g/m² 813 811 825 811 789 Caliper mm 1.53 1.55 1.63 1.54 1.51 Density Kg/m² 530 522 505 526 524 Formation variability % 6.6 4.9 3.4 6.3 7.8 Energy required kJ/kg 76 54 40 76 75 Energy reduction % 29 47 — — Fluff dry bulk 0.6 kPa 51.3 51.1 46.3 52.4 52.7 cc/g Fluff dry bulk 2.5 kPa 24.7 25.2 23.6 25.9 25.8 cc/g Wick time, seconds 2.1 2.1 2.1 2.2 2.3 Wicking rate mm/sec. 12.9 12.8 12.5 12.7 12.2 Fluff wet bulk 2.5 kPa 9.6 9.2 8.9 9.7 9.6 cc/g Fluff wet bulk 0.6 kPa 10.7 10.2 9.9 10.7 10.6 cc/g Capacity g/g 10.4 9.8 9.2 10.4 10.3

It can be seen that the fiberization energy in columns 2 and 3 are far less than those in columns 1, 4 and 5 while the fiberization energy in columns 4 and 5 are about the same as the control in column 1. The wicking times and wicking rates in all of the columns are about the same.

EXAMPLE 2

The fiberization energy of pulp containing elongate sub-micron diameter precipitated calcium carbonate, whether from NanoMaterials Technology or SOCAL from Solvay, SA., is far less than either a control pulp sheet without additives. At the same addition rate the NanoMaterials Technology and SOCAL elongate sub-micron diameter precipitated calcium carbonate had the same fiberization energy. The wicking times or wicking rates of pulp containing elongate sub-micron diameter precipitated calcium carbonate were slightly greater than the control pulp sheet. The shape of the elongate sub-micron diameter precipitated calcium carbonate did not matter. This is shown in Table 2.

Hand sheets were made on a 12″ by 12″ handsheet former using once dried CF 416 pulp at a targeted basis weight of 750 g/m². Table 2 shows the results. In column 1, the control was once dried CF 416 pulp. In column 2, a target of 10% elongate sub-micron diameter precipitated calcium carbonate from NanoMaterials Technology having a mean length of 4 microns was added to the once dried CF 416 pulp In column 3, a target of 10% elongate sub-micron diameter precipitated calcium carbonate (SOCAL 90) was added to the once dried CF 416 pulp. In column 4, a target of 10% elongate sub-micron diameter precipitated calcium carbonate (SOCAL 92) was added to the once dried CF 416 pulp. The amount of elongate sub-micron diameter precipitated calcium carbonate added was based on the total weight of the sheet.

TABLE 2 1 2 3 4 Basis weight g/m² 944 943 947 985 Caliper mm 1.58 1.58 1.60 1.59 Density Kg/m² 596 596 593 620 Formation variability % 8.3 7.6 6.4 7.1 Energy required kJ/kg 107 79 89 79 Energy reduction % 26 17 26 Fluff dry bulk 0.6 kPa 54.6 47.8 48.5 47.9 cc/g Fluff dry bulk 2.5 kPa 26.5 24.0 24.8 24.3 cc/g Wick time, seconds 2.2 1.8 1.9 1.8 Wicking rate mm/sec. 13.3 14.6 14.0 14.5 Fluff wet bulk 2.5 kPa 9.9 9.1 9.2 9.1 cc/g Fluff wet bulk 0.6 kPa 11.1 10.1 10.3 10.3 cc/g Capacity g/g 10.9 9.7 9.8 10.0

EXAMPLE 3

The fiberization energy of once dried pulp containing elongate sub-micron diameter precipitated calcium carbonate is far less than either a control pulp sheet without additives or a pulp sheet containing other additives. This is shown in a comparison of elongate sub-micron diameter precipitated calcium carbonate and Tech 4, Tech 8 and Vansil 20 at a target of 5% by weight addition to the once dried pulp.

Hand sheets were made on a 12″ by 12″ handsheet former using NB 416 pulp at a targeted basis weight of 750 g/m². The results of the comparison are shown in Table 3. In column 1, the control was NB 416 pulp. In column 2, a target of 5% elongate sub-micron diameter precipitated calcium carbonate having a mean length of 4 microns was added to the once dried NB 416 pulp. In column 3, a target of 5% Tech 4 was added to the once dried NB 416 pulp. In column 4, a target of 5% Tech 8 was added to the once dried NB 416 pulp. In column 5, a target of 5% Vansil 20 was added to the once dried NB 416 pulp. The amount of elongate sub-micron diameter precipitated calcium carbonate or additive added was based on the total weight of the sheet. It can be seen that the fiberization energy for the elongate sub-micron diameter precipitated calcium carbonate was superior to the control or the samples with Tech 4, Tech 8 or Vansil 20 pigments and the wicking rate for the elongate sub-micron diameter precipitated calcium carbonate is the same as for the pigments.

TABLE 3 1 2 3 4 5 Basis weight g/m² 758 782 771 788 791 Caliper mm 1.29 1.30 1.26 1.33 1.33 Density Kg/m² 590 601 611 592 594 Formation variability % 5.9 7.7 4.4 6.4 6.0 Energy required kJ/kg 86 59 84 84 79 Energy reduction % 31 2 2 8 Fluff dry bulk 0.6 kPa 50.9 51.0 53.2 51.6 50.7 cc/g Fluff dry bulk 2.5 kPa 25.7 25.9 26.3 25.5 25.2 cc/g Wick time, seconds 2.5 2.1 2.0 2.0 2.1 Wicking rate mm/sec. 11.3 13.5 14.3 13.9 13.4 Fluff wet bulk 2.5 kPa 9.5 9.2 9.7 9.5 9.7 cc/g Fluff wet bulk 0.6 kPa 10.7 10.2 10.8 10.7 10.7 cc/g Capacity g/g 10.6 10.0 10.5 10.2 10.5

EXAMPLE 4

The same additives as those used in Table 3 were also compared at a 10% weight addition. Hand sheets were made on a 12″ by 12″ handsheet former using once dried NB 416 pulp at a targeted basis weight of 750 g/m². The results of the comparison are shown in Table 4. In column 1, the control was once dried NB 416 pulp. In column 2, a target of 10% elongate sub-micron diameter precipitated calcium carbonate having a mean length of 4 μm was added to the once dried NB 416 pulp. In column 3, a target of 10% Tech 4 was added to the once dried NB 416 pulp. In column 4, a target of 10% Tech 8 was added to the once dried NB 416 pulp. In column 5, a target of 10% Vansil 20 was added to the once dried NB 416 pulp. The amount of elongate sub-micron diameter precipitated calcium carbonate or additive added was based on the total weight of the sheet. Again the fiberization energy of the elongate sub-micron diameter precipitated calcium carbonate was far superior to the control or the additives while the wicking rate of the elongate sub-micron diameter precipitated calcium carbonate was comparable to the additives.

TABLE 4 1 2 3 4 5 Basis weight g/m² 758 837 816 843 830 Caliper mm 1.29 1.40 1.33 1.33 1.37 Density Kg/m² 590 599 612 634 606 Formation variability % 5.9 6.4 3.8 7.0 7.1 Energy required kJ/kg 86 43 78 78 79 Energy reduction % 50 9 9 9 Fluff dry bulk 0.6 kPa 50.9 45.7 51.8 49.6 50.6 cc/g Fluff dry bulk 2.5 kPa 25.7 23.3 26.1 25.2 25.0 cc/g Wick time, seconds 2.5 1.9 2.0 2.1 2.2 Wicking rate mm/sec. 11.3 13.6 14.2 13.0 12.7 Fluff wet bulk 2.5 kPa 9.5 8.7 9.7 9.1 9.6 cc/g Fluff wet bulk 0.6 kPa 10.7 9.6 10.7 10.2 10.6 cc/g Capacity g/g 10.6 9.1 10.4 9.9 10.4

As can be seen from the examples elongate sub-micron diameter precipitated calcium carbonate greatly reduces the fiberization energy of a pulp sheet while maintaining the wicking performance of the resultant air-laid pad.

EXAMPLE 5

Samples were made using never dried NB 416 cellulose pulp fiber with (1) no sub-micron diameter precipitated calcium carbonate (control), with (2) SOCAL 90A (PCC1) sub-micron diameter precipitated calcium carbonate added to the slurry at targets of 5% and 10% of the oven dry weight of the sheet, with (3) SOCAL P2 (PCC2) sub-micron diameter precipitated calcium carbonate added to the slurry at targets of 5% and 10% of the oven dry weight of the sheet, and with (4) NanoMaterials Technology (NMT) sub-micron diameter precipitated calcium carbonate (NPCC) added to the slurry at targets of 5% and 10% of the oven dry weight of the sheet. No retention aid was used the sub-micron diameter precipitated calcium carbonate. The results are given in Table 6 and 7 and in FIGS. 7-15. The ash content in FIG. 8 is the amount of elongate sub-micron diameter calcium carbonate retained on the sheet.

Table 5 shows the results of the 5% addition tests in which the target amount of sub-micron diameter precipitated calcium carbonate is targeted at 5% of the weight of the sheet. Column 1 is the never dried NB 416 pulp control; column 2 is a target of 5% PCC1 added to the never dried NB 416 pulp; column 3 is a target of 5% PCC2 added to the never dried NB 416 pulp and column 4 is a target of 5% NPCC from NanoMaterials Technology added to never dried NB 416 pulp.

TABLE 5 1 2 3 4 Actual ash content, % 0.19 3.63 1.88 3.89 Energy required, kj/Kg 130.6 102.4 112.9 97.7 Energy reduction % 22 14 25 Dry bulk 0.6 kPa, cc/g 53.7 50.6 51.4 51.8 Dry bulk 2.5 kPa, cc/g 27.6 26.1 26.2 27.1 Wick time, sec. 2.67 2.10 2.07 2.23 Wicking rate, mm/sec 11.3 13.4 13.8 13.0 Wet bulk 2.5 kPa 10.3 9.53 9.74 9.66 Resat bulk 11.32 10.63 10.82 10.81 Capacity, g H₂O/g pulp 11.21 10.36 10.64 10.63

Table 6 shows the results in which the target amount of sub-micron diameter precipitated calcium carbonate is 10% of the weight of the sheet. Column 1 is the never dried NB 416 pulp control; column 2 is a target of 10% PCC1 (12.5% of PCC1) added to the never dried NB 416 pulp; column 3 is a target of 10% PCC2 added to the never dried NB 416 pulp and column 4 is a target of 10% NPCC from NanoMaterials Technology added to never dried NB 416 pulp.

The fiberization energy was greatly reduced with use of the elongate sub-micron diameter precipitated calcium carbonate was reduced from 25% to 42%. The wicking rate increased from 11.3 to 14.1 mm/sec.

TABLE 6 1 2 3 4 Actual ash content, % 0.19 6.02 1.88 3.89 Energy required, kJ/kg 130.6 85.0 97.4 75.1 Energy reduction % 35 25 42 Dry bulk 0.6 kPa, cc/g 53.7 46.9 46.6 50.2 Dry bulk 2.5 kPa, cc/g 27.6 24.7 25.0 26.2 Wick time, sec. 2.67 2.03 1.93 2.00 Wicking rate, mm/sec 11.3 13.2 14.0 14.1 Wet bulk 2.5 kPa 10.3 9.13 9.28 9.38 Resat bulk 11.32 10.25 10.33 10.50 Capacity, g H₂O/g pulp 11.21 9.87 10.17 10.18

Hand sheets were made on a 12″ by 12″ handsheet former using once-dried CF 416 pulp at a targeted basis weight of 100 g/m². The pulp was mixed in a British Disintegrator for 5 minutes. It was then diluted to about 0.5% consistency. The pulp was ten placed in the former and air couched. The handsheet was pressed at 20 psi on a screen with top and bottom blotters. It was run through a Gess Press at 100 psi with top and bottom blotters, and dried in a drum dryer at 350° F. for 10 minutes on each side. The sub-micron diameter precipitated calcium carbonate was added to the pulp after the pulp consistency was lowered and before the hand sheet formation. The combination mixed for one minute. The 4 micron average length sub-micron diameter precipitated calcium carbonate was used at targeted 10% and 40% of the weight of the oven dried pulp addition

The softness was measured using the TAPPI test method T543 of 94 for Gurley stiffness.

Pulp test samples were 1 inch wide and 3½ inches long. The samples were test with a 5 g weight 1 inch from the center.

The control 12 inch by 12 inch handsheet had 9 g of pulp. The control test sample cut from the handsheet had a Gurley stiffness of 331.6 mg.

The first test 12 inch by 12 inch handsheet was targeted for the sub-micron diameter precipitated calcium carbonate being 5% of the weight of the pulp. The handsheet had 8.55 g of pulp and 0.45 g of submicron precipitated calcium carbonate. The test sample cut from the handsheet had a Gurley stiffness of 250.0 mg. There was a 25% decrease in Gurley stiffness.

The second test 12 inch by 12 inch handsheet was targeted for the sub-micron diameter precipitated calcium carbonate being 10% of the weight of the pulp. The handsheet had 8.1 g of pulp and 0.9 g of submicron precipitated calcium carbonate. The test sample cut from the handsheet had a Gurley stiffness of 90.0 mg. There was a 73% decrease in Gurley stiffness.

The Gurley stiffness was substantially lower when sub-micron diameter precipitated calcium carbonate was added to the pulp.

It will be understood that changes can be made without departing from the spirit of the invention. 

1. A wet laid cellulose pulp sheet comprising wet-laid cellulose fiber and elongate precipitated calcium carbonate having a diameter of 0.015 to 0.6 microns at its maximum diameter and a length of 1 to 10 microns and the elongate precipitated calcium carbonate is incorporated within the sheet.
 2. The wet laid cellulose pulp sheet of claim 1 wherein the elongate precipitated calcium carbonate is present in the amount of 3 to 45% of the weight of the cellulose pulp.
 3. The wet laid cellulose pulp sheet of claim 1 wherein the elongate precipitated calcium carbonate is present in the amount of 3 to 15% of the weight of the cellulose pulp.
 4. The wet laid cellulose pulp sheet of claim 1 wherein the elongate precipitated calcium carbonate is 1 to 3 microns in length.
 5. The wet laid cellulose pulp sheet of claim 1 wherein the elongate precipitated calcium carbonate is 3 to 6 μm in length.
 6. The wet laid cellulose pulp sheet of claim 1 wherein the fiberization energy is reduced from 20% to 50% as compared with a wet laid cellulose pulp sheet not having a fiberization agent. 7 The wet laid cellulose pulp sheet of claim 6 wherein the wicking value is substantially the same as compared with a wet laid cellulose pulp sheet not having a fiberization agent.
 8. The wet laid cellulose pulp sheet of claim 1 wherein the Gurley stiffness is from 20 to 80% less as compared with a wet laid cellulose pulp sheet not having a fiberization agent.
 9. The wet laid cellulose pulp sheet of claim 1 wherein the elongate precipitated calcium carbonate is 0.015 to 0.45 microns in diameter at its maximum diameter.
 10. The wet laid cellulose pulp sheet of claim 9 wherein the elongate precipitated calcium carbonate is 1 to 3 microns in length.
 11. The wet laid cellulose pulp sheet of claim 9 wherein the elongate precipitated calcium carbonate is 3 to 10 microns in length.
 12. The wet laid cellulose pulp sheet of claim 9 wherein the elongate precipitated calcium carbonate is present in the amount of 3 to 45% of the weight of the cellulose pulp.
 13. The wet laid cellulose pulp sheet of claim 9 wherein the elongate precipitated calcium carbonate is present in the amount of 3 to 15% of the weight of the cellulose pulp.
 14. The wet laid cellulose pulp sheet of claim 9 wherein the elongate precipitated calcium carbonate is 1 to 3 microns in length.
 15. The wet laid cellulose pulp sheet of claim 9 wherein the elongate precipitated calcium carbonate is 3 to 6 μm in length.
 16. The wet laid cellulose pulp sheet of claim 9 wherein the fiberization energy is reduced from 20% to 50% as compared with a wet laid cellulose pulp sheet not having a fiberization agent. 17 The wet laid cellulose pulp sheet of claim 9 wherein the wicking value is substantially the same as compared with a wet laid cellulose pulp sheet not having a fiberization agent.
 18. The wet laid cellulose pulp sheet of claim 9 wherein the Gurley stiffness is from 20 to 80% less as compared with a wet laid cellulose pulp sheet not having a fiberization agent. 